The invention relates to dichromatic and trichromatic dyestuff compositions for dyeing polyamides. Commercial dyeings are normally made using several component dye mixture in order to obtain the desired shade and color depth. These dye mixtures comprise dyes selected from the primary colors; i.e. a yellow, a blue and a red dye. The individual dyes must be suitable for combination dyeing in trichromatic systems; i.e. blends two or more dyes containing the primary colors mixed predetermined amounts to give the desired shade. Suitable dyes in admixture must also produce a uniform color build-up and simultaneously a uniform shade at different dye bath concentrations in order to produce a dye having an acceptable appearance. In addition, the dye composition must give a dyeing having acceptable fastness properties at an acceptable cost.
In commercial practice, polyamide fibers are dyed by the exhaust, continuous, and printing methods using acid dyes. An illustrative trichromatic, acid dye system is a mixture of a C.I. (Color Index) Acid Orange 156, C.I. Acid Blue 324, and C.I. acid Red 266. Although, these systems have gained acceptance in the dyeing of polyamides, they lack certain desired characteristics, e.g. on tone build-up, cold strike rate, ozone and nitrous oxide resistance, little or no phototropism and cold water solubility.
Various attempts have been made to use dyes containing the vinyl sulfone group to dye nylon. However, these dyes have not gained commercial acceptance in the dyeing of polyamide primarily due to their failure to give a uniform level dyeing with the above described properties. The vinyl sulfone dyes tend to selectively concentrate on one portion of the fiber leaving other portions deficient in that color either due variations in the fiber's morphology or the strike rate of the dye or a combination of both. This problem is particularly evident in the dyeing of polyamide materials where the fiber is highly extended, for example, in nylon carpets and rugs.
Various attempts have been tried to overcome disadvantages of the vinyl sulfone dyes in polyamide dyeing applications. U.S. Pat. No. 4,762,524 is an example of the prior art. In this prior art patent, a reaction product of the vinyl sulfone dye and an N-alkyl-amino-alkyl sulfonic or carboxylic acid is formed in an attempt to make the vinyl sulfone dye more suitable for polyamide dyeings. U.S. Pat. No. 3,802,837 teaches to form a reaction product of N-methyl-taurine to adapt the vinyl sulfone dye to polyamide dyeing. Although the above identified prior art teaches improved dyeing characteristics, they have not been accepted in the commercial dyeing of polyamides.
This invention is directed to a simple method of overcoming the problems of the prior art without resorting to modification of the chemical structure of vinyl sulfone dyes. It has been found, that the compositions of this invention provide the stated requirement and provide superior polyamide dyeing with excellent fastness, low phototropism, high ozone and nitrous resistance.